I will be visiting Switzerland on the 26th of April. My itinerary is like this.

26th- Day 1 - reach Basel around 10 am. Then take train to interlaken and reach lauterbrunnen.

Stroll in Lauterbrunnen at leisure.

27th Day 2: Take cable car to Grrutschalp and hike to Murren. Cable car to Sclithorn

Come down to Gimmelwald and further to Stechelberg using cable cars and then walk back through the beautiful valley

28th Day 3: Train to Wengen and cable car to Manlichen and from there cable car to grindelwald, back by train to Lauterbrunnen.

29th Day 4: Flight is at 3:45pm from Basel.

Kindly advice if any of the cable cars or transportation means will not be available during my visit as per the above itinerary. I heard about maintenance work in some part. Kindly confirm so that I can plan my trip.

Alternatives depend on the amount of snow left when you're there. It might be possible to walk from the train stop Alpiglen down to Grindelwald, for example. Do note that this is a 600 m descend, so a bit hard on the knees. You can of course walk in the other direction as well. You can check the conditions at any tourist office when you're there, and they will also know about alternatives. Staffed train stations can also offer help.